摘要
云南洱源地区地处青藏高原东南缘的滇西北地区中部,区内地质构造复杂,多条断裂交会穿过,且地热活动活跃,显示出很强的断裂构造特征。地区内地震活动频繁,2013年以来在维西-乔后-巍山断裂西侧发生了多个5级以上地震。文中利用云南区域固定台网和滇西北密集台阵记录的2008年1月1日—2023年7月20日发生在洱源地区的地震走时数据,采用波速比模型一致性约束的双差层析成像方法,获得了云南洱源及其周边区域的地壳三维V_(P)、V_(S)和V_(P)/V_(S)模型及地震重定位结果。结果表明:1)在龙蟠-乔后断裂以东,维西-乔后-巍山断裂、红河断裂和鹤庆-洱源断裂交会处聚集了大量小地震,缺乏中强地震。从现有的层析成像结果分析认为浅层发生的部分小地震可能与地热流体无直接关系,而从浅层向深层逐渐变高的V_(P)/V_(S)值可能暗示深部存在流体,深部流体可能在循环流动过程中逐渐渗透到浅层岩石中,并与部分密集小地震的发生有关。2)2013年以来发生的4个5级以上地震均发生在维西-乔后-巍山断裂西侧,并呈NNW-SSE走向分布,表明川滇块体西边界断裂系统的地震危险性有所增大。3)2013年3月3日和4月17日发生的洱源地震序列主要位于低V_(P)、低V_(S)和低V_(P)/V_(S)值的异常体内。一般而言,如存在流体,则V_(S)比V_(P)下降得更快,从而导致高V_(P)/V_(S)值,而低V_(P)/V_(S)则表明低V_(S)并非由流体所致。因此,现有的成像证据表明地震序列所处区域并不存在流体,从而推断地震序列的发生与流体无直接关系。空间上与洱源地震序列接近的2017年3月27日M_(S)5.1漾濞地震序列也具有相同的速度结构特征,因此也可能与流体无直接联系。2016年5月18日发生的M_(S)5.1云龙地震序列的主震和部分余震主要位于高V_(P)、高V_(S)和V_(P)/V_(S)相对高值区内,高V_(S)表明并非因存在流体而导致出现相对高的V_(P
The Eryuan area is located in the central part of the northwest Yunnan region on the southeastern edge of the Qinghai-Xizang Plateau.The geological structure in the area is complex,including the Weixi-Qiaohou-Weishan Fault and Honghe Fault,as well as the Longpan-Qiaohou Fault and Heqing-Eryuan Fault,which intersect in an“X”shape.The geothermal activity in the area is also active and exhibits strong fault structural characteristics.Earthquake activity is also frequent in the Eryuan area.Since 2013,multiple earthquakes with M_(S)≥5.0 have occurred on the west side of the Weixi-Qiaohou-Weishan Fault.Given the complex geological and geothermal background and seismic activity in the Eryuan area,we use the seismic travel time data recorded by the Yunnan Regional Seismic Network and the Northwest Yunnan Dense Array from January 1,2008,to July 20,2023,V_(P)/V_(S) model consistency-constrained DD tomography method to obtain the 3D V_(P),V_(S),and V_(P)/V_(S) models and relocation results in the Eryuan and its surrounding areas.The research results indicate that:1)based on the relocation results,the dense small seismic cluster develops at the intersection of the Weixi-Qiaohou-Weishan Fault,Honghe Fault,and Heqing-eryuan Fault deserves special attention.Four earthquakes with M_(S)≥5.0 that have occurred since 2013 are mainly distributed on the west side of the Weixi-Qiaohou-Weishan Fault,with an NNW-SSE trend distribution.The fault system at the western boundary of the Sichuan-Yunnan block is very complex,and its seismic risk deserves our special attention.2)Based on the tomography results,the widely distributed low-velocity anomalies in the upper crust of the study area may be related to the crustal material migration pathway caused by the escape of the Sichuan-Yunnan diamond block towards SSE.3)Combining imaging results with geochemical research results for inference,the high V_(P)/V_(S) below 10km depth beneath the small seismic cluster at the intersection of the Weixi-Qiaohou-Weishan Fault,Honghe Fault,and Heqin
作者
曹颖
钱佳威
黄江培
周青云
CAO Ying;QIAN Jia-wei;HUANG Jiang-pei;ZHOU Qing-yun(Yunnan Earthquake Agency,Kunming 650224,China;College of Oceanography,Hohai University,Nanjing 210098,China;School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)
出处
《地震地质》
EI
CSCD
北大核心
2024年第1期162-183,共22页
Seismology and Geology
基金
国家重点研发计划项目(2021YFC3000600)
云南省重点研发计划项目(202203AC100003)
国家自然科学基金(42304056)共同资助。
